This application claims the priority benefit of Taiwan application serial No. 87102080, filed Feb. 16, 1998, the full disclosure of which is incorporated herein by reference.
1. Field of Invention
The present invention relates to a wafer burn-in testing method. More particularly, the present invention relates to a wafer burn-in testing method for testing all the components in a wafer.
2. Description of Related Art
FIG. 1 is a simplified diagram showing the manufacturing of an integrated circuit chip from a silicon wafer to final packaging. As shown in FIG. 1, after a series of steps for fabricating integrated circuits on a semiconductor wafer, a circular wafer 2 having a cut-away edge originally for facilitating alignment is produced. Because wafer fabrication produces a large number of individual chips 4 whose electrical properties may vary considerably, each of these chips 4 needs to be tested electrically. In general, a plurality of bonding pads 6 is formed on the periphery of each chip serving as testing points and/or subsequent connection. These bonding pads 6 can be used for testing the chips in two ways. First, before the wafer is cut up into individual dies or chips, mechanical probes can be used to form electrical contact with the bonding pad. Therefore, each chip 4 within the wafer can be individually electrically tested. Alternatively, after the wafer is cut into individual chips 8, wires can be bonded to the bonding pads 6. Then, the whole chip 8 can be enclosed within a package 10, and finally an integrated circuit (IC) package 12 or a large-scale integration (LSI) is formed. Electrical testing of the chip 8 can be carried out with ease after a complete package is formed because automatic testing machines can tap from the fixed external terminals and conduct the burn-in testing.
To connect from the bonding pads of a wafer chip to external terminals, a medium such as a wire or a bump must be used. FIG. 2 is a diagram showing a wire bonding method of connecting from the bonding pads on a wafer chip to external packaging. FIG. 3 is a diagram showing a tape-automated bonding (TAB) method of connecting from the bonding pads on a wafer to external packaging. FIG. 4 is a diagram showing a flip chip (FC) method of connecting from the bonding pads on a wafer to external packaging. In the wire bonding method as in FIG. 2, a piece of fine metallic wire is used to connect one of the bonding pads on the wafer chip to an external metal lead. In the tape-automated bonding method shown in FIG. 3, a piece of tape is used for connecting a bump on a bonding pad of a wafer chip to an external metal lead. In the flip chip (FC) method shown in FIG. 4, a solder bump between a bonding pad and a circuit film is used to connect the wafer chip to the external metallic terminals.
FIGS. 5A through 5G are cross-sectional views showing the progression of manufacturing steps needed to produce a bump. First, as shown in FIG. 5A, passivation layers 22 are formed on each side of aluminum bonding pad 20. Next, as shown in FIG. 5B, a titanium (Ti) layer 24 having a thickness of about 1000 xc3x85 is formed over the aluminum pad 20 and the passivation layers 22. Thereafter, a copper (Cu) layer 26 having a thickness of about 4000 xc3x85 is formed over the titanium layer 24. Then, as shown in FIG. 5C, a photoresist layer 28 having a thickness of between 30 xcexcm to 40 xcexcm is formed over the copper layer 26. Subsequently, using a mask 32 having chromium pattern 30 on it, a portion of the photoresist layer 28 is exposed to ultraviolet (UV) light. In the subsequent step, as shown in FIG. 5D, the exposed photoresist layer 28 is removed by etching to form a trench 34. After that, as shown in FIG. 5E, a layer of copper 36 with a thickness of about 8 xcexcm is first deposited into the trench 34. Next, either lead-tin (SnPb) or gold (Au) solder is poured into the trench 34 forming a mushroom-shaped structure 38. Later, as shown in FIG. 5F, the photoresist layer 28 on each side of the mushroom-shaped lead-tin solder 38 is removed. Finally, as shown in FIG. 5G, a bump with a hemispherical-shaped upper profile is formed after further chemical treatment.
FIG. 6 shows the general IC layout for carrying out conventional burn-in testing. As shown in FIG. 6, a chip 48 in the middle is connected to external terminals for testing through a back plate 40 containing testing pads 42, inner-leads 44, outer-leads 46 and outer-leads holes 50. Therefore, a high-quality IC or LSI is obtained by first sawing the fabricated wafer into dies, then forming each die into a package, and finally the packaged product has to pass a burn-in test. The above procedure for obtaining a good die is known commonly as a known good die (KDG) method. Although the KDG method can obtain highly functional packages, the testing cost is exceptionally high because each chip has to be tested individually. Moreover, whenever a defect is found during testing, the whole package has to be scrapped leading to more waste due to cost spent on packaging.
In light of the foregoing, there is a need for a better burn-in testing method for wafers.
Accordingly, the present invention is to provide a method for testing the whole wafer so that defective wafer chips are detected and scrapped before the wafer is used for packaging. Hence, packaging cost can be saved and yield of packaged IC can be increased considerably.
In another aspect, this invention provides a method for testing the whole wafer by meshing the bonding pads on a tape-automated bonding (TAB) tape with bumps on the wafer so that complicated circuits can be avoided. In other words, the capacity to design two or more layers of internal circuits on a TAB tape is utilized such that internal circuits for carrying out the burn-in testing of the whole wafer can be greatly simplified.
In yet another aspect, this invention provides some tooling (fixtures) and a mechanism (suction caused by drawing a vacuum) for tightly engaging the bumps on the wafer with the pads on the TAB tape. Moreover, when the burn-in testing is finished, the TAB tape and the tooling can be used repeatedly for checking other wafers, one at a time. Therefore, the cost of operation is reduced to a minimum.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for carrying out wafer burn-in testing. The method comprises the steps of first providing a wafer and then forming a plurality of bumps on the wafer. Next, a tape-automated bonding (TAB) tape having a plurality of bonding pads is designed and fabricated. Each bonding pad has an external contact point and is electrically connected with an internal circuit. Pressure is applied to the wafer so that the bumps on the wafer can make contact with the bonding pads on the TAB tape. Subsequently, voltages and currents can be supplied to various bonding pads through the tape to carry out burn-in testing necessary for the whole wafer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.